The present invention relates to a picture transmission method, a picture transmission method program, a storage medium which stores the picture transmission method program, and a picture transmission apparatus. More particularly, the invention relates to techniques for distributing a moving picture stream over a network. According to the invention, picture data as a whole are first transmitted when compressed at a high compression rate. Based on position information acquired from a given transmission destination, part of the picture data representing a partial picture region is transmitted at a higher resolution than the remaining regions. That is, a user-designated partial region of each picture is compressed at a reduced data compression rate for a moving picture streaming service, so that users may watch desired portions of the streaming moving pictures reproduced at a higher resolution.
Conventionally, moving picture streams are distributed over a network such as the Internet using a real-time compression and transmission system such as MPEG4 (Moving Picture Experts Group Phase 4).
MPEG4 represents techniques for efficiently compressing moving picture data through the effective use of correlations between continuous pictures. Where moving picture data streams are distributed using MPEG4, the data compression rate is varied depending on the current amount of encoded data so that the data may be transmitted at a bit rate commensurate with the capacity of communication lines being used.
With such a real-time compression and transmission system in use, higher data compression rates necessarily increase the amount of the data dropped from the original moving picture data and a transmission destination may not be able to reproduce clear pictures (i.e. pictures of high qualities). On the other hand, reduced data compression rates eventually make it impossible to transmit moving picture data over communication lines that have limited capacities.
One proposed solution (ROI) to the above problem involves reducing the data compression rate for only a specific region of each moving picture. In other words, only that part of each picture which users are presumably desirous of watching at higher quality is transmitted at higher resolution while the remaining portions which users do not need in detailed picture, such as background, are left to have lower quality. The conventional solution is supposed efficiently to transmit moving picture data over communication lines subject to limited capacities.
One disadvantage of the solution above is that the specific region of each picture selected for the high-resolution transmission may differ from the one that is desired by a user. Different users have different preferences. In a football game broadcast, for example, some users may look for a detailed picture of a particular player on defense side while other users may prefer watching a high-resolution image of another player on offence side.
Transmitting picture portions that are not desired by a user at high resolution may be wasteful. Under the conventional scheme, a number of users may miss high-quality images of their preference.
As outlined above, if only a fixed region of each picture is compressed at a reduced data compression rate for higher-quality distribution over the network by a moving picture streaming service, some users are satisfied but others are not. The conventional method has failed to address the diverse user preferences where pictures are transmitted on a partial-region enhanced-quality basis.
The present invention has been made in view of the above circumstances and provides a picture transmission method, a picture transmission method program, a storage medium which stores the picture transmission method program, and a picture transmission apparatus for adequately addressing user preferences so that a user-designated specific region of each picture is compressed at a lower data compression rate for higher-resolution distribution through a moving picture streaming service.